I climbed that vertical shaft in the secret passage 9 years ago.
I free climbed the short pitch up to the dam from Grand Turk and threw a rope down for the other two in my group. If I remember, there was an old chisel wedged in a crack which helped me climb it. There were no other ropes there and no sign that anyone had been there for a while.
The vertical shaft was a couple of hundred feet along the passage and was indeed dug from top down and around 100ft deep. At the top, you find yourself at the end of a level running parallel with the level below. It runs around 15ft to a very old and solid collapse (possibly a collapsed or back-filled shaft or stope). Pulling stuff out just caused more to fall in. I'm not saying it couldn't be dug but it would take a lot of work, especially not knowing what you are digging in to.
There are two videos of it on Youtube, one was dragging the gear through the crawl and the other was while I was actually climbing. Both videos are embarrassingly poor quality and the climb isn't very interesting and basically just shown me struggling to sort out my method of climbing. The actual climb took me 8 hours without a break as once I had started I was pretty committed. I managed to drill one hole 1/2" deep as it was quartz and the rubbish drill I had died
. This was about 20ft up and completely useless. I ended up climbing the shaft without bolting. I noticed one drill hole about 40ft up but no bolt or hanger. It was obviously old and I wonder if it was drilled back in the days when the original timber ladder was a bit more intact and someone got to the top of the ladder and tried to put a bolt in..?
There was a pointed rock at the top which I wrapped the rope around as a pull through to abseil back down. As it didn't look like it would be worth returning I didn't leave a rope in place. I also didn't want to risk anyone climbing a rope that was simply thrown over a pointy rock
If you are desperate, you will find the videos here...